That sounds super complicated. I'd rather this not be made into a type of spreadsheet. ^^;
But working with what you're saying:
Tier 1a is best of the best. Eg, top 1%
Tier 1b is ... top 3%?
Tier 1c needs to probably be Indisputable Top-5 of a given character.
That said, have to be careful with this. A lot of people play really really poor support characters (especially Sedna) or don't split monks well. I may specialize in Sedna, sure, but the only character I really struggle with while playing is Rook. Even though any tier 1a or 1b might be able to play all the characters proficiently, some people just don't LIKE certain characters and so play them maybe only "average".
However, since these players also have top-notch map awareness and have good skill builds and good exposure, it matters less. It doesn't matter WHO you are, if you port 3v1 on someone with 1k hp, you're gonna get a kill. But, you aren't making the most of your character and doing the crazy bullshit you might be doing because you know the abesolute limit of your character and if you're pushing it or not.
Also, the more popular characters (Rook, Reg, UB, Erebus, Oak), it's hard to say you're a "Top 5". Too many people play them well and play them differently.
Even though I consider myself a Top 5 Sedna, my favorite build has faults and weaknesses. I know how to adapt and shift my build depending on who I'm fighting and what they are doing, but, still, it's not my "comfort" build. So, other people with different builds than me in a situation that I don't like might perform better than me.
2a is top 10%?
2b is top 10% with a specific character. Should that not have to be Rook-LE-UB-Oak? What if they are a really awesome Oak?
I'm against having a Tier 3 for a specific character. Tier 3 is more of a "Honorable Mention" and puts someone on a watchlist. "You got this random guy on you're team, you can trust him to play at least decently. If you see him improve and start to kick ass, maybe he should be Tier 2." I don't think that Tier 3 should have a requirement to be well-balanced in your character selection.